Alien life as we have imagined it over the years

Capt. Kirk vs. the silicon-based lifeform known as the Horta. One of the more innovative images of alien life … since at the very least it isn’t bipedal like many of the aliens we are prone to envision.

Encyclopaedia Britannica/MultipleMartian meteorite Alh84001. "Does it carry microbial fossils from Mars or are its strange features just the product of some unique geochemistry? After almost 20 years, dueling papers are still coming out, and the opposing parties are no closer to a resolution," reports Astrobiology magazine.

Getty Images/MultipleScientists at the Johnson Space Center in Houston, Tx., said in 2001 that a crystallized magnetic mineral, called magnetite, found in a Martian meteorite is similar to crystals formed on Earth by bacteria. "I am convinced that this is supporting evidence for the presence of ancient life on Mars," said Kathie Thomas-Keprta, an astrobiologist at the Space Center.

Upper figure: Modern magnetotactic bacteria, one showing a chain of magnetite crystals, as seen in the backscattered scanning electron microscope.
Lower figure: Magnetite crystals and chains of magnetite crystals in the Martian meteorite Alh84001. One conspicuous chain indicated by arrows. (Photo By Getty Images/Getty Images)